Field of the Invention
The present invention relates to a distance measurement technique, and, more particularly, to a technique to measure distance information from a plurality of images image-captured with different image-capturing parameters.
Description of the Related Art
As a technique to acquire distance of an image-capturing scene from an image acquired by an imaging apparatus, the depth from defocus (DFD) method, disclosed in Japanese Patent Application Laid-open No. 2013-044844, has been proposed. According to the DFD method, a plurality of images having a different degree of blur is acquired by controlling the image-capturing parameters of an imaging optical system, and the degree of blur and the correlation amount of the acquired plurality of images are calculated using the measurment target pixel and its peripheral pixels in the plurality of images.
Since the degree of blur and correlation amount change depending on the distance of an object in the image, the distance can be calculated using this relationship. An advantage of the distance measurement by the DFD method is that incorporation with commercially available imaging apparatuses is possible because distance can be calculated by one imaging system.
Even if an object is image-captured at high-speed with changing of the image-capturing parameters during image-capturing, displacement is generated among the plurality of images due to camera shake, object motion, or the like, which drops the distance measurement accuracy of the DFD method. To prevent positional displacement, the positions of the images are aligned before executing the DFD method. Known methods to align positions are, for example, a block matching method disclosed in Japanese Patent Application Laid-open No. 2013-044844, and a method using an affine transformation disclosed in Japanese Patent Application Laid-open No. 2008-310418.